There is one party leader who can look forward with confidence to Thursday's elections and referendum. Is David Cameron the man with reasons to be cheerful? The Conservatives may lose council seats, but they will probably not do so badly that reverses can't be shrugged off as the level of bruising to a government that must be expected when the economy is fragile and taxes are being hiked and spending slashed in the name of dealing with the deficit.

Truth to tell, Mr Cameron has not been losing any sleep over the fate of Tory councillors. He has much more at stake in the referendum. First past the post has generally been good for the Tories by inflating minority support in the country into majorities at Westminster. It gave most of the 20th century to the Conservatives. But at the beginning of the campaign, the Tory leader did not regard the referendum as a matter of life or death. Then he and George Osborne suddenly panicked. In my interview with Nick Clegg for the New Reviewsection of today's Observer, the Lib Dem leader says the prime minister and chancellor became frightened that they would face a revolt by the Tory right. The deputy prime minister squarely blames the Tory leadership for the venomous name-calling into which the campaign has descended. Mr Clegg tells me that Messrs Cameron and Osborne made the decision to "throw the kitchen sink" at preserving first past the post.

If recent opinion polls are right, the scares and smears have worked. Senior Tories I've spoken to in the past few days are increasingly bullish that they will be on the winning side. Still, they cannot be sure of the result until they actually know it. And even if electoral reform is killed, Mr Cameron will not have a smooth ride after Thursday. He will have to try to kiss and make up with the Lib Dems, who are likely to get a whole lot more bolshy if AV goes down, to stabilise and sustain the coalition. Whatever happens on Thursday, the post-voting environment will be a tricky one for the prime minister to navigate.

So if David Cameron is not the leader looking forward to Thursday, is it Nick Clegg? Obviously not unless he is clinically insane. A victory for AV would be a boost and the more so for now being regarded by bookies and pollsters as a remote possibility. It doesn't have to be so if the Yes side can use the last stretch of the campaign to focus the minds of voters on the real issues at stake. But if the polls are an accurate forecast of what will happen in the elections and the referendum, Friday is not going to be the best day of the Lib Dem leader's life.

With both the coalition partners having reason to be fearful about the fall-out from Thursday, it would be natural to conclude that Ed Miliband is the leader who is feeling lucky. On the face of it, he has a message of potent simplicity. To all those voters who fear the coalition or hate what it is doing or just want to send a warning to them not to go too far, Mr Miliband urges a vote for Labour as the only national party capable of opposing the coalition. What's more, Labour activists are fired up for the fight – or ought to be. After 13 years in government, when they had to play defensive in midterm elections, now they can go on the offensive.

Labour's opinion poll share has greatly improved on the dismal 29% it scored at the general election a year ago. Everyone expects Labour to make gains, possibly up to a 1,000 council seats in England. The Lib Dems look especially vulnerable in the more northern parts of Britain where hostility towards the coalition tends to be most intensely visceral. A great night on Thursday could be the platform for Ed Miliband to declare that he has completed the first phase of his party's recovery and is ready to move on to the next.

Momentum, a very useful commodity in politics, ought to be with him. But Labour has problems, the biggest of which is called Scotland. They ruled in Edinburgh in coalition with the Lib Dems for the first eight years of the devolved parliament. When they lost control to the Nationalists in 2007, ending a half century of Labour domination in Scotland, it was a shock. But many expected it to be a temporary interregnum before Scotland returned to Labour rule. Quite a lot has gone wrong for Alex Salmond since he formed a minority government four years ago. As with the Lib Dems at Westminster, it has been a bumpy transition for the Nats from being a party of perpetual protest into becoming a party of power. They had long contended that an independent Scotland could thrive alongside smaller nations in the European Union. The legs of that argument were cut off by the financial crisis. The terrible bust suffered by the Republic of Ireland no longer makes it look like such a great role model. Then there was Sir Fred Goodwin's ruination of the Royal Bank of Scotland, which would no longer exist had not the English taxpayer been available to provide the money to bail it out.

Labour was confident that Scotland would default back to its historic masters, especially once the Tories, a party with few friends north of the border, were in power at Westminster. This complacent assumption seemed justified until quite recently. But in a matter of a few months double-digit poll leads over the Nationalists have evaporated like Scotch mist. It is now the SNP which sits on a commanding lead. The Nats may even do well enough to take seats from Labour. Some of this is down to the skill of Mr Salmond who is the answer to the question with which I opened this column.

The one-time chippy outsider has turned himself into a "father of the nation" figure. He has downpedalled independence and fought a presidential campaign. "SNP – Alex Salmond for first minister" is the party's slogan on the ballot papers. He attended the royal wedding. I am pretty confident that the SNP leader is no monarchist; his party are republicans at heart. Yet there he was grinning from a pew in Westminster Abbey, using the occasion to "represent my nation" and boost his presidential aura. Labour's leader north of the border, Iain Gray, is a man with all the charisma that is suggested by his surname. As a consequence of a dreadful campaign, some believe he is even threatened with the loss of his East Lothian seat.

It wouldn't be terribly fair to blame a Labour defeat in Scotland on Ed Miliband, but he would nevertheless suffer collateral damage. It is undermining of the Labour leader's claim to represent progressive Britain if Scots have concluded that the Nationalists will do a better job of protecting their interests from the London coalition.

Some of the shadow cabinet fear there is a wider lesson from the shock Labour collapse in Scotland, a lesson that Mr Miliband ought to heed. The fate of Scottish Labour demonstrates that playing safe is actually highly risky. There is great peril in boring leadership which does little more than mouth anti-government rhetoric and sit back on an opinion poll lead. Scotland shows how that can give an illusion of success which will evaporate at the moment of choice, especially when up against a wily and ruthless incumbent.

Turning to the referendum, on the face of it Ed Miliband has little to lose. If AV is defeated, Nick Clegg will be in trouble. If AV is the winner, it causes even bigger problems for David Cameron. Yet it seems to me rather superficial to regard it as a win either way for Mr Miliband. He has campaigned for AV. He has told his party that it needs to see beyond its antagonism towards the Lib Dems and focus on the longer-term, progressive interest in adopting a fairer voting system. That is a message he needs to amplify over the next four days because the result may well turn on how Labour supporters split between backing reform and voting no. If the Labour antis are responsible for the defeat of AV, then it is bound to reflect on Mr Miliband that his party has spurned its leader's advice.

When Britain wakes up on Friday morning, the political map will look like a multicoloured patchwork quilt. If the polls are broadly right, there will be a Nationalist government in Scotland; a Labour government or Labour-led coalition in Wales; Labour will be in charge of most of the big English cities except London; the capital will have a Tory mayor; a Conservative-Liberal Democrat coalition will continue to govern at Westminster. These different administrations will have been selected by a variety of electoral systems, giving the lie to the No campaign's patronising claim that Britons are too stupid to do anything more sophisticated than mark a cross in a box.

Even if that sort of awful argument succeeds in preserving first past the post, the map of many colours will remind us that Britain is no longer a two-tribe nation. That may be a sliver of consolation for Nick Clegg on what, unless AV is won, will be a bad night for him. And it ought to give food for thought to both Ed Miliband and David Cameron.